A driveline of a hybrid vehicle may include an internal combustion engine, an electric motor, and a transmission to propel the vehicle. The hybrid vehicle may stop engine and motor rotation during some conditions to conserve electrical and chemical energy. For example, engine and motor rotation may be stopped when the vehicle stops to reduce fuel consumption and electrical charge consumption. However, it may be desirable to hold the driveline in a condition that helps to hold the vehicle stationary after the vehicle is stopped. For example, it may be desirable to couple the transmission output shaft to the transmission case and vehicle chassis to reduce the possibility of vehicle motion. The transmission output shaft may be coupled to the transmission case via one or more applied transmission clutches. Thus, it may be desirable to keep one or more transmission clutches applied during a vehicle stop. One way to keep transmission clutches applied when the engine and motor are not rotating is to supply transmission fluid to transmission clutches via an electric pump. The electric pump is operated at a higher speed to maintain transmission fluid line pressure, but the electric pump may consume more electrical energy than is desired.
The inventors herein have recognized the above-mentioned issues and have developed a driveline operating method, comprising: adjusting a speed of an electric transmission pump via a controller in response to a rotational stop position of a mechanically driven transmission pump.
By adjusting speed of an electric transmission fluid pump in response to a rotational stopping position of a mechanically driven transmission fluid pump, it may be possible to provide the technical result of reducing energy consumed by the electric transmission fluid pump while providing sufficient output pressure to maintain operating states of transmission clutches. For example, speed of the electric transmission fluid pump may be adjusted to a speed that is sufficient to overcome internal leakage of fluid within the transmission and maintain clutch operating state while not operating at too high of a speed to excessively consume electrical power.
The present description may provide several advantages. In particular, the approach may provide improved vehicle energy efficiency. Further, the approach may provide desired transmission functionality when the transmission torque converter is not rotating. Additionally, the approach may be applied to find energy efficient rotational stopping positions for the mechanical transmission pump.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.